1. Field of the Invention
The present invention relates to an external seal structure of a vacuum valve including a valve body containing a valve part, a cylinder cover containing a drive part, and a partition wall member including an upper end plate held between the valve body and the cylinder cover, in which an annular seal member is placed between the upper end plate and the valve body to prevent external leakage of fluid.
2. Related Art
In a semiconductor manufacturing device, for example, material gas is supplied to a reaction chamber and this reaction chamber is evacuated by a vacuum pump to produce a thin film or coating on a wafer while keeping the reaction chamber in a vacuumed state. A vacuum valve is placed at an outlet of the reaction chamber to control an exhaust speed so as not to raise or kick up particles in the reaction chamber during exhaust in order to prevent adhesion of the particles to the surface of the wafer.
FIG. 11 is a cross sectional of a conventional vacuum valve 101. The vacuum valve 101 includes a valve body 104 and a cylinder cover 107 which are connected, forming an outer appearance of the vacuum valve 101. The vacuum valve 101 is configured so that a drive part 106 imparts a drive force to a valve element 102 through a drive shaft 105, thereby bringing the valve element 102 into or out of contact with a valve seat 103 to control a fluid flow. In the valve body 104, a partition wall member 108 is placed to prevent leakage of material gas toward the drive part 106.
The partition wall member 108 has a bellows 108a and an upper end plate 108b connected to an upper end of the bellows 108a. This partition wall member 108 is further provided with a thick wall portion 108c protruding toward the cylinder cover 107 (upward in FIG. 11) from an outer edge of an end face of the upper end plate 108b facing the cylinder cover 107. The valve body 104 is provided, at its upper end in FIG. 11, with a first joint part 104a in which the upper end plate 108b is fitted. On the other hand, the cylinder cover 107 is provided, at its lower end in FIG. 11, with a second joint part 107b provided with a shoulder portion 107a in which the thick wall portion 108c is fitted. The valve body 104 and the cylinder cover 107 support the upper end plate 108b positioned in place in a radial direction through the thick wall portion 108c. Between the first joint part 104a and the upper end plate 108b, there is placed an annular seal member 109 made of fluorinated resin to prevent external leakage of the material gas (see Patent Document 1, for example).
The above vacuum valve 101 is subjected to a leak test to detect leakage of the annular seal member 109 after product assembling, after circuit mounting, during maintenance of the semiconductor manufacturing device, and others. This leak test is generally conducted in such a manner that the internal pressure of the vacuum valve 101 is reduced to a background value and then an operator sprays fluid used for a test (“test fluid”) to a joint section between the valve body 104 and the cylinder cover 107. A leak test device senses an amount of the test fluid in the vacuum valve 101 (i.e., measures a leak measurement value) and detects leakage of the test fluid through the annular seal member 109. It should be noted that helium gas (He gas) is generally used as the test fluid. This He gas is so small in molecular diameter as to easily get into a leaking area, so that even leakage of a small amount of fluid can be detected.
In the leak test, in a case where the leak measurement value continues to decrease until a predetermined detection time is elapsed from start of spraying of He gas, which indicates that the He gas does not leak from the annular seal member 109, the annular seal member 109 is not determined to be abnormal. On the other hand, in a case where the leak measurement value increases within the predetermined detection time, which indicates that the He gas leaks from the annular seal member 109, the annular seal member 109 is determined to be abnormal. According to this leak test, the leakage of the annular seal member 109 can be inspected without disassembling the vacuum valve 101.